Currently, a time division long term evolution (TD-LTE) network attracts much attention because of various advantages of the TD-LTE network such as a high data transmission rate, high spectrum efficiency, and flexible spectrum allocation.
Referring to Table 1, Table 1 shows seven uplink-downlink subframe configuration manners that correspond to an LTE network in a TDD system.
TABLE 1Uplink-downlink configuration of a TDD systemUplink-downlinkDownlink-to-uplinkSubframe numberconfiguration numberswitch-point periodicity012345678905 millisecondsDSUUUDSUUU15 millisecondsDSUUDDSUUD25 millisecondsDSUDDDSUDD310 milliseconds DSUUUDDDDD410 milliseconds DSUUDDDDDD510 milliseconds DSUDDDDDDD65 millisecondsDSUUUDSUUD
In Table 1, 0 to 6 represent seven different configuration identifiers, U represents an uplink subframe, D represents a downlink subframe, and S represents a special subframe used to complete switching between an uplink subframe and a downlink subframe.
In the TD-LTE network, duration corresponding to each subframe is one millisecond. Referring to Table 1, the TDD uplink-downlink configuration 0 includes a smallest quantity of downlink subframes, that is, only two downlink subframes are included in a subframe 0 to a subframe 9; and it can be known from Table 1 that each downlink-to-uplink switch-point periodicity (which is five milliseconds) includes only one downlink subframe.
In an LTE system, a user terminal needs to perform radio resource management (RRM) such as an intra-frequency measurement, an inter-frequency measurement, or an inter-RAT measurement. In a process of the intra-frequency measurement, because a to-be-measured center frequency corresponding to user equipment (UE) does not change, a connection to an original serving cell does not need to be disrupted. However, in a process of the inter-frequency measurement or the inter-RAT measurement, because a to-be-measured center frequency corresponding to the UE deviates, a user needs a “gap” period, which is referred to as a Gap. In the Gap, the connection to the original serving cell is disrupted, a frequency channel number is adjusted to be on a target center frequency, a measurement is performed on the target center frequency, and an adjustment back to the original center frequency is performed when the Gap ends. Currently, Gap types supported by the LTE network are shown in Table 2.
TABLE 2Gap types supported by an LTE user terminalMinimum available timefor an inter-frequencyMeasurementMeasurementmeasurement or inter-RATGap PatternGap lengthGap repetitionmeasurement during 480ID(MGL, ms)period (MGRP, ms)ms period (Tinter1, ms)Measurement purpose064060Inter-FrequencyE-UTRAN FDD andTDD, UTRAN FDD,GERAN, LCR TDD,HRPD, CDMA2000 1x168030Inter-FrequencyE-UTRAN FDD andTDD, UTRAN FDD,GERAN, LCR TDD,HRPD, CDMA2000 1x
The Gaps shown in Table 2 above are applicable to both an FDD-LTE system and a TDD-LTE system. Specifically, both the FDD-LTE system and the TDD-LTE system have a measurement Gap length of six ms, but different systems correspond to different repetition periods.
In a process of an inter-frequency measurement or an inter-RAT measurement, in the six ms corresponding to the foregoing Gap, there is approximately one ms for UE to perform a radio frequency adjustment (a center frequency adjustment, or the like), and the remaining five ms is used for the UE to perform an inter-frequency measurement or an inter-RAT measurement. For the TDD system, the five ms for the inter-frequency measurement is further limited, as shown in Table 3.
TABLE 3Quantity of uplink/downlink subframes needed by a TDD -LTE system having different Gap configurationsNumber ofInter-frequencyuplink/downlinkDownlink pilotmeasurement period ofMeasurementsubframes per halftimeslot (DwPTS)an LTE time divisionbandwidthframe (5 ms)NormalExtendedduplex systemConfiguration[RB]DLULCPCP(TMeasurement—Period—TDD—Inter [ms])062219760 · Ts20480 · Ts480 × Nfreq1 (Note 1)502219760 · Ts20480 · Ts240 × Nfreq(Note 1):This configuration is optionalNote 2:Ts is defined in 3GPP TS 36.211 [16]
It can be known from Table 3 that regardless of a value of a bandwidth during a TDD measurement, two downlink subframes are needed in every five ms to satisfy an RRM measurement requirement. However, in the TDD uplink-downlink configuration 0, there is only one downlink subframe in every five ms. Therefore, a current RRM measurement requirement is not applicable to the TDD uplink-downlink configuration 0, and consequently, the UE cannot perform an RRM measurement on a cell whose TDD uplink-downlink configuration identifier is 0.
To sum up, currently there exists a problem that in a process of an inter-frequency measurement or an inter-RAT measurement in a TDD system, UE cannot perform an RRM measurement on a cell whose TDD uplink-downlink configuration identifier is 0.